Processor errors in controllers that control or regulate functions that are critical with regard to safety must be detected by monitoring. The controllers with safety functions are conventionally used for anti-lock control systems, traction control systems and/or driving dynamics control systems. Self-test, plausibility monitoring and watchdog methods are known for use in single-computer controllers.
Methods and measuring equipment for measuring the quiescent current (IDDQ) are used for manufacturer testing of CMOS components (integrated circuits, IC). The testing is described, for example, in the article "Parallel heiBt schnell", (Parallel means fast) Markt und Technik, Wochenzeitung fur Elektronik (Market and Technology, Weekly Journal of Electronics), no. 36 of Sep. 1, 1995, page 58. The background of the quiescent current test is that in a digital CMOS component in a purely static logic, almost the entire power loss occurs in its interior during switching operations. In an idle state, the current flow is limited to tiny leakage currents and currents due to pull-up or pull-down resistance at the inputs and external loads at the output drivers. Many manufacturing-related errors lead to increased conductivity between the positive and negative power supply voltage. If such defective regions (point errors) in a circuit are activated, it leads to a sudden increase in current consumption. Such errors can be detected by a highly precise measurement of current consumption during the test procedure and comparison with suitable setpoints. Such a quiescent current measurement is utilized in the production of CMOS components to sort out the defective components after the manufacturing process.
Utilizing the above described controllers with safety functions, it is customary to provide two computers that check on each other mutually by parallel computing and/or plausibility tests to increase reliability. Cost considerations suggest using only one computer in these controllers.
The object of the present invention is to increase the reliability in operation with a control unit having safety functions.